Fuel cell stack systems (hereinafter fuel cells) are increasingly being used as a power source for electric vehicles and other applications. Different fuel cell types can be provided such as phosphoric acid, alkaline, molten carbonate, solid oxide, and proton exchange membrane (PEM), for example.
In proton exchange membrane (PEM) fuel cells, a hydrogen gas reactant is supplied as a fuel to an anode side of the fuel cell and an oxygen gas reactant is supplied as an oxidant to a cathode side of the fuel cell. The reaction that occurs between the reactant gases in the fuel cell consumes the hydrogen at the anode side and produces product water at the cathode side.
The basic components of a PEM-type fuel cell are two electrodes separated by a polymer membrane electrolyte. Each electrode is coated on one side with a thin catalyst layer. The electrodes, catalyst, and membrane together form a membrane electrode assembly (MEA). The MEA is typically sandwiched between “anode” and “cathode” diffusion media or diffusion layers that are formed from a resilient, conductive, and gas permeable material such as carbon fabric or paper. The diffusion media serve as the primary current collectors for the anode and cathode as well as providing mechanical support for the MEA.
The diffusion media and MEA are pressed between a pair of electronically conductive plates which serve as secondary current collectors for collecting the current from the primary current collectors. The plates conduct current between adjacent cells internally of the fuel cell stack in the case of bipolar plates and conduct current externally of the stack in the case of unipolar plates at the end of the stack.
The bipolar plates typically include two thin, facing metal sheets. One of the sheets defines a flow path on one outer surface thereof for delivery of the fuel to the anode of the MEA. An outer surface of the other sheet defines a flow path for the oxidant for delivery to the cathode side of the MEA. When the sheets are joined, a flow path for a dielectric cooling fluid is defined. The plates are typically produced from a formable metal that provides suitable strength, electrical conductivity, and corrosion resistance, such as 316 alloy stainless steel, for example.
The fuel cell stack, which may contain more than one hundred plates, is compressed, and the elements held together by bolts through corners of the stack and anchored to frames at the ends of the stack. In order to militate against undesirable leakage of fluids from between the pairs of plates, a seal or gasket is often used. The seal is typically disposed along a peripheral edge of the pairs of plates. Prior art seals have included the use of an elastomeric material. Additional prior art seals have included the use of a metal seal, such as disclosed in published Patent Cooperation Treaty (PCT) Pat. Appl. No. PCT/EP2003/011347, hereby incorporated herein by reference in its entirety.
Efficient operation of PEM fuel cells may depend on an amount of electrical resistance present in the system, and more particularly to the electrical resistance at an interface between the bipolar plates and the diffusion media of the MEA.
It is desirable to produce a fuel cell adapted to minimize electrical resistance between the bipolar plates and the MEA of a fuel cell assembly to optimize system performance. In the fuel cell described herein, efficient operation of the fuel cell is maximized by adhering diffusion media adjacent a membrane electrode assembly to adjacent bipolar plates with an electrically conductive adhesive layer.